Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos oponentes havia quando o recorde era de 6-0?
 ###Tabelas: CREATE TABLE season_3_1998–99 (season_3_1998–99_id AUTO_INCREMENT PRIMARY KEY, Series # INT, Season # INT, Title VARCHAR, Directed by VARCHAR, Written by VARCHAR, Original air date VARCHAR) CREATE TABLE list_of_coaches_by_club (list_of_coaches_by_club_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Nationality VARCHAR, Club VARCHAR, From INT, Until VARCHAR) CREATE TABLE tournament_champions (tournament_champions_id AUTO_INCREMENT PRIMARY KEY, Year VARCHAR, Champion (seed) VARCHAR, Score VARCHAR, Runner-up (seed) VARCHAR, Most valuable player VARCHAR) CREATE TABLE schedule (schedule_id AUTO_INCREMENT PRIMARY KEY, Game INT, Date VARCHAR, Opponent VARCHAR, Result VARCHAR, Cowboys points INT, Opponents INT, Record VARCHAR) CREATE TABLE performances_and_result (performances_and_result_id AUTO_INCREMENT PRIMARY KEY, Week # VARCHAR, Theme VARCHAR, Song choice VARCHAR, Original artist VARCHAR, Order # VARCHAR, Result VARCHAR)  
SELECT Date FROM schedule WHERE Record = 6-0